muscle fibres and its significance

1. MUSCLE FIBRES AND ITS SIGNIFICANCE
BY: DR. AKASH JAINTH
MPT

2. SKELETAL MUSCLE FIBERS CAN BE CLASSIFIED
BASED ON TWO CRITERIA:.
How fast do fibers contract relative to others
How do fibers regenerate ATP.

3. Type 1: Slow oxidative (SO) fibers
contract relatively slowly and use
aerobic respiration (oxygen and
glucose) to produce ATP. They
produce low power contractions
over long periods and are slow to
fatigue.
Type 2 B: Fast glycolytic (FG)
fibers have fast contractions
and primarily use anaerobic
glycolysis. The FG fibers
fatigue more quickly than the
others[3].
Type 2 A: Fast oxidative (FO)
fibers have fast contractions
and primarily use aerobic
respiration, but because
they may switch to
anaerobic respiration
(glycolysis), can fatigue more
quickly than SO fibers.

4. TYPE 1 FIBERS
These fibers have a rich capillary supply,
numerous mitocondria and aerobic
respiratory enzymes, and a high
concentration of myoglobin.
Myoglobin is a red pigment, similar to the
haemoglobin in red blood cells, that
improves the delivery of oxygen to slow
twitch fibres. Because of their high
myoglobin content, slow twitch fibers also
called red fibers.
The fact that SO fibers can function for long
periods without fatiguing makes them useful in
maintaining posture, producing isometric
contractions, stabilizing bones and joints, and
making small movements that happen often but
do not require large amounts of energy. They do
not produce high tension, and thus they are not
used for powerful, fast movements that require
high amounts of energy and rapid cross-bridge
cycling

5. TYPE 2A
Type 2A (FO) fibers are
sometimes called intermediate
fibers because they possess
characteristics that are
intermediate between fast
fibers and slow fibers.
They produce ATP relatively
quickly, more quickly than SO
fibers, and thus can produce
relatively high amounts of
tension. They are oxidative
because they produce ATP
aerobically, possess high
amounts of mitochondria, and do
not fatigue quickly. However, FO
fibers do not possess significant
myoglobin, giving them a lighter
color than the red SO fibers.
FO fibers are used primarily for
movements, such as walking,
that require more energy than
postural control but less energy
than an explosive movement,
such as sprinting. FO fibers are
useful for this type of movement
because they produce more
tension than SO fibers but they
are more fatigue-resistant than
FG fibers.

6. TYPE 2B
Type 2B (FG) fibers primarily use
anaerobic glycolysis as their ATP source.
They have a large diameter and possess
high amounts of glycogen, which is used
in glycolysis to generate ATP quickly to
produce high levels of tension. Because
they do not primarily use aerobic
metabolism, they do not possess
substantial numbers of mitochondria or
significant amounts of myoglobin and
therefore have a white color.
FG fibers are used to produce rapid,
forceful contractions to make quick,
powerful movements. These fibers
fatigue quickly, permitting them to only
be used for short periods

7. SPEED OF CONTRACTION
The speed of contraction is dependent
on how quickly myosin’s ATPase
hydrolyzes ATP to produce cross-bridge
action.
Fast fibers hydrolyze ATP
approximately twice as rapidly as slow
fibers, resulting in much quicker cross-
bridge cycling (which pulls the thin
filaments toward the center of the
sarcomeres at a faster rate).
eg. The extraocular muscles that
position the eyes have a high
proportion of fast-twitch fibers and
reach maximum tension in about 7.3
msec (milliseconds—thousandths of a
second). The soleus muscle in the leg,
by contrast, has a high proportion of
slow-twitch fibers and requires about
100 msec to reach maximum tension

8. AGEING
Age-related loss of muscle mass results primarily
from a decrease in the total number of both type I
and type II fibers and, secondarily, from a
preferential atrophy of type II fibers.
Atrophy of type II fibers leads to a larger proportion
of slow type muscle mass in aged muscle, as
evidenced by slower contraction and relaxation
times in older muscle.
In addition, the loss of alpha motoneurons with age
results in some reinnervation of“abandoned”
muscle fibers by adjacent motor units that may be
of a different type. This may facilitate fiber type
conversion, as the reinnervated muscle fibers take
on the properties of the new“parent” motor unit

9. MUSCLE METABOLISM
ATP provides the energy for
muscle contraction. The
three mechanisms for ATP
regeneration are creatine
phosphate, anaerobic glyco
lysis, and aerobic
metabolism.
Creatine phosphate
provides about the first
15 seconds of ATP at the
beginning of muscle
contraction.
Aerobic metabolism utilizes
oxygen to produce much
more ATP, allowing a muscle
to work for longer periods
Muscle fatigue, which has
many contributing factors,
occurs when muscle can
no longer contract.

10. PHYSIOTHERAPY
Physical therapy interventions can
affect muscle fiber types leading
to improvements in muscle
performance. Physical therapy
interventions can be broadly
divided into those designed to:
Increase the patient's resistance
to fatigue. Training that places a
high metabolic demand on the
muscle (endurance training) will
increase the oxidative capacity of
all muscle fiber types, mainly
through increases in the amount
of mitochondria,
aerobic/oxidative enzymes, and
capillarization of the trained
muscle.
Increase the patient's force production.
High-intensity resistance training (eg,
high-load–low-repetition training)
results in changes in fiber type similar
to those seen with endurance training,
although muscle hypertrophy also plays
an essential role in producing strength
gains. Initial increases in force
production with high-intensity
resistance training programs are largely
mediated by neural factors, rather than
visible hypertrophy of muscle fibers, in
adults with no pathology or
impairments. Even so, changes
in muscle proteins, such as the myosin
heavy chains, do begin after a few
workouts, but visible hypertrophy of
muscle fibers is not evident until
training is conducted over a longer
period of time (>8 weeks).

11. REFRENCES
▪ Scott W, Stevens J, Binder–Macleod SA. Human skeletal muscle fiber type classifications. Physical therapy. 2001 Nov
1;81(11):1810-6.Available: https://academic.oup.com/ptj/article/81/11/1810/2857618(accessed 30.11.2021)
▪ ↑ Jump up to:2.0 2.1 Openoregon state ed. 10.5 Types of Muscle
Fibers Available: https://open.oregonstate.education/aandp/chapter/10-5-types-of-muscle-fibers/(accessed 30.11.2021)
▪ ↑ Jump up to:3.0 3.1 3.2 3.3 3.4 3.5 Opentext BC Types of muscle
fibres Available:https://opentextbc.ca/anatomyandphysiologyopenstax/chapter/types-of-muscle-fibers/(accessed 30.11.2021)
▪ ↑ Sports science insider Muscle Fibres explained Available:https://sportscienceinsider.com/muscle-fibers-explained-slow-fast-
twitch/ (accessed 1.12.2021)
▪ ↑ Jump up to:5.0 5.1 79 steps health Slow and Fast Twitch Fibers Available: https://www.78stepshealth.us/human-physiology/slow-
and-fasttwitch-fibers.html (accessed 30.11.2021)
▪ ↑ Mt Hood Muscle Fiber Types Availablehttps://mhcc.pressbooks.pub/hpe295/chapter/muscle-fiber-types/ (accessed
30.11.2021)
▪ ↑ Wisegeek What is a motor neurone. Available from; https://www.thehealthboard.com/what-is-a-motor-neuron.htm(accessed
1.12.2021)
▪ ↑ Openstax Homeostasis Available:https://openstax.org/books/anatomy-and-physiology/pages/1-5-
homeostasis?query=muscle%20metabolism&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-
id2226448 (accessed 30.11.2021)

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